Abstract

Spider bites are a common challenge for physicians and veterinarians worldwide. Envenomation by the Western Black Widow (Latrodectus hesperus) is frequently associated with a necrotic cutaneous reaction at the bite site; a condition known as necrotic arachnidism. Although the composition of venom is known to be almost entirely neurotoxic, and thus, presumably not damaging to skin, varying degrees of dermal necrosis are commonly encountered at the site of envenomation. The underlying mechanism is unknown, prompting our investigation of the possibility for a bacterial etiology of the local lesions associated with the bite. This descriptive study reports the presence of 5 uncommon, highly pathogenic; multiple antibiotic resistant, bacterial species cultured from 220 pairs of sterilely extracted black widow spider fangs. This finding is consistent with the known unresponsiveness of cutaneous spider bite lesions to steroids and first-line antibiotic treatment; which has led to the misconception that the venom is the causative agent. This discovery supports our hypothesis that bacterial strains have adapted to life on the fangs of certain spiders; providing them with an excellent mode of infection by not only being passed subcutaneously to the victim, but also protected from host defenses by the immunosuppressive effects of the venom. Since current treatment protocols for spider envenomations concentrate almost solely on the local and systemic effects of the venom itself, our findings suggest that the current diagnostic algorithm and treatment standards for spider bites in both human and animal medicine may be inadequate and should be re-assessed.